The present invention relates generally to decoding, and more particularly, to cyclic decoding for cascaded forward error-correction FEC codes.
Future intelligent optical transport networks (OTNs) should possess the capability of dynamic data rate adjustment. One solution is to adjust data rate by changing the overhead of the adopted forward-error-correction (FEC) codes while keeping other system configurations unchanged. Meanwhile, to meet the increasing high demand on data rate, low-density-parity-check (LDPC) codes have been proved to be promising candidates for high-speed OTNs. Therefore rate-adaptive LDPC-coded modulation [1],[2], becomes an essential component for future OTNs.
Prior techniques for cascaded rate-adaptive forward-error correction (FEC) codes efficiently solve the hardware-consuming issue related with conventional rate-adaptive FEC schemes. However, the coding gain of cascaded FEC is usually smaller than that of an optimally designed FEC of comparable overhead. As both the hardware cost and performance are critical in modern high-speed and high-capacity optical communications, it is highly desirable to have rate-adaptive FEC with both low-cost as cascaded FEC and high coding gain as the optimally designed FEC.
The following references discuss prior adaptive FEC techniques in optical communications. See [1] G.-H. Gho, L. Klak, and J. M. Kahn, “Rate-adaptive coding for optical fiber transmission systems,” J. Lightw. Technol., vol. 29, no. 2, pp. 222-233, January 2011. [2] M. Arabaci, I. B. Djordjevic, R. Saunders, and R. M. Marcoccia, “Polarization-multiplexed rate-adaptive non-binary-LDPC-coded multilevel modulation with coherent detection for optical transport networks,” Optics Express, vol. 18, pp. 1820-1832, January 2010.
No existing work in adaptive FEC in optical communications has been able to address the hardware cost issue while maintaining sufficient large coding gain at the mean time. In reference [1], adaptive hard-decision FEC was proposed based on repetition schemes which itself resulted in non-optimal codes and hence incurred degradation in coding gain. In reference [2], a rate-adaptive FEC was proposed based on specifically designed low-density parity-check (LDPC) codes of different overheads. Large coding gain was achieved but the relevant high hardware cost was not considered.
Accordingly, there is a need for a for cyclic decoding that overcomes the limitations of existing techniques.